Compositions for treating aluminum surfaces



2 1 CROSS REFERENCE ,WMINLE United States Patent 0 "ice 3,510,430 Patented May 5, 1970 3510430 surface into contact with an aqueous solution of the COMPOSITIONS For: TIIEATING ALUMINUM SURFACES Percent by weight Floyd L. Mickelson and Robert W. Bland, Chicago, Ill., F i lf t 50.75

2 3 :533 gz s Corporaflon, Chmgo, 111-, a 5 Alkali metal bisulfate 5-30 Alkali metal nitrate 5-24 No Drawmg' :332 g gg z 640370 Alkali metal silicofiuoride 1-8 US- C 252-79-1 8 Claims with the percentages being on an anhydrous basis. Aque- 10 ous solutions of such compositions will deoxidize and desmut aluminum quickly. ABSTRACT OF THE DISCLOSURE The novel aqueous solutions provided by this invention Provided are compositions and Solutions containing dissolve oxides and surface impurities without detrimenferric sulfate, an alkali metal bisulfate, an alkali metal tally attackmg the P f nitrate and an alkali metal silicofiuoride for desmutting Furthermqe by mcluduig one or more silrfactams m aluminum Surfaces the compositions, precleamng of the aluminum before deoxidizing it can be eliminated and both cleaning and deoxidizing effected simultaneously.

This invention relates to the art of treating metal sur- Either sodium bisulfate potassium i i or i faces. More particularly, this invention is concerned with hires i f be used m the F p spdlum novel compositions and processes for treating the surblsuifade 1S advlsiably because It less .expenslve' faces of aluminum and aluminum based alloys to condi- Sodmm mate or potassium nitrate or fion Such surfaces for subsequent treatment tures thereof can be used but for economic reasons so- One of the ways of preparing the surface of aluminum dmm 5 prefyredt for further processing is to etch the surface in an alkali 5 elthFr sodmm sllcofluonde or f solution. After etching, a fine particulate material remains or mxtures can used i compos" on the surface of the aluminum. This material is referred tlons' For cost reasons. Sodlum 1S f f to as The material is dusHike loosely held on Although other fluorldes were tried in the compositions the surface and often can be easily rubbed off. The comas Subsmutes for slhcofluonges i 9 them were position of the smut varies with the alloy but generally found to be a satlsfactPry solimm blfiuonde tended to is composed of the oxides of any alloying metals, includetch the alummuni and '9 aluminum alloys such as 2024 ing silicon oxide, as well as aluminum oxide and those 606.1 47 i etchmg produced smut Also metallic compounds that do not dissolve during the etchsodium 'i i q gave f deoxidlzmg results i ing. The smut dulls the metal surface and, if not removed, sodmm lfiuonde m composltlons Whlch were otherwlse subsequent deposits of chemical conversion coatings, such 35 as descilbed as chromate coatings or paint applications, will not be mch'islon of an alkah metal nitrate the m uniform and will be loosely held where the smut is not Hons IS an "P P f.eatu.re of mvemlon' The mtrate removed. overcomes pitting, which 1s a particularly common prob T e tmen f aluminum alloy Surfaces with convem lem 1n deoxidlzrng certam aluminum alloys, one such be 40 mg 6061-T6. tional acid deoxidizers fails to satisfactorily remove high Th d b temperature oxides formed during various fabricating and e g i i e y t mvemlm} are Raddy forming operations. A solution of nitric acid or chromic i by mtenmxmg the usmg pY acid is commonly used for this purpose- Such Solutions tional procedures. For ready handling, the compositions are highly reactive and within 30 seconds can etch the are advlsably as granular surface to such a degree as to render it unfit for further Although be used p broad processing. Even when carried out carefully, subsequent range of mgredlems as prevlously i F {Suany chemical coatings are irregular and far from satisfactory. more .advamageouf to employ composltlons wlthm the Chromic acid type deoxidizers also cause disposal probfollowmg amounts lems because of the stream pollution they can cause. F 1f Percent by welght Chemical deoxidizers are not only used to remove ate 50'70 smut but also to prepare aluminum surfaces for subse- Zi metal b.lsulfate quent resistance welding. For such preparation, a prior i metal i i 1040 caustic etch is not required in most instances so no smut a 1 metal lcofiuonde 14 is formed to be removed afterwards by the deoxidizer. The compositions of this invention are conveniently Deoxidizers are accordingly used to prepare the aluminum used in treating aluminum according to novel methods surface immediately after precleaning to remove dirt and employing novel working solutions or use solutions pregrease. An effective deoxidizer for this purpose must repared by dissolving the compositions in water. move surface oxides effectively to reduce electrical resist- Novel working solutions are suitably produced by disance to acceptable levels for producing secure welds with solving a sufiicient amount of a composition of this inminimum power consumption. vention in water to provide 4.0 g. to 45.0 g. of nitrate ions According to the present invention, there are provided per gallon, 0.4 g. to 15.0 g. of fluoride ions per gallon, novel compositions and methods which can be used to 0.4 g. to 2.0 g. of hydrogen ions per gallon and 8.0 g. to desmut or deoxidize aluminum surfaces. 60.0 g. of ferric ions per gallon. Such working solutions It has been found that the surfaces of aluminum can can be used to deoxidize and desmut aluminum surfaces. be deoxidized and desmutted by bringing the aluminum On a more readily calculable basis, it is generally suitable to dissolve from about 2 to 16 ounces of the composition per gallon of water to form a suitable working solution.

Treatment of aluminum surfaces with such working solutions can be effected at any suitable temperature. Generally, solution temperatures from about room temperature to 180 F. are most suitable with immersion contact times of from about 0.5 to 10 minutes being sufiicient. Following treatment, the aluminum surface can be rinsed with water and air dried.

EXAMPLE 1 A solid. granular composition is prepared by intermixing the following ingredients:

Ingredients: Percent by weight Ferric sulfate 59.0 Sodium bisulfate 21.0 Sodium nitrate 15.0 Sodium silicofiuoride 5.0

Such a composition gives rapid, thorough desmutting of aluminum after alkali etching. It is most suitably used on aluminum alloys that do not have a high silicon content.

Working solutions of the composition are prepared by dissolving about 2 to 16 ounces of the composition per one gallon of water. The working solutions are used at about room temperature (70-80 F.).

Prior to desmutting, the aluminum object is recleaned to remove dirt and grease and then etched with a caustic etch bath followed by a water rinse. An etching bath can comprise about 6 ounces of alkali per gallon at a temperature of l40-l50 F. An etching time of 3 minutes is suitable.

Following the alkali etching the aluminum object can be dipped into the desmutting working solution at 75 F. The time needed to effect desmutting will vary with the aluminum alloy being treated and the concentration of the working solution as shown by the following table.

1 The composition of some of these alloys is as follows:

4.5% Cu, 1.5% Mg, 0.6% Mn, bal. A1.

1.2% M11, bal. A1.

2.5% Mg, 0.25% Cr, bal. Al.

1% Mg, 0.6% Si, 0.25% Cu, 0.25% Cr, bel. A1. 0.7% Mg, 0.4% Si, bal. Al.

7075-0 and 7075-T6 5.5% Zn, 2.5% Mg, 1.5% Cu, 0.3% Cr,bal.Al.

The desmutting times given above are those required if no agitation is given during the desmutting operation. Moderate agitation during desmutting will reduce the times required by approximately 25%.

The desmutting working solutions can also be used to deoxidize aluminum surfaces prior to resistance welding.

(1) Deoxidizing unetched aluminum surfaces The aluminum surfaces are cleaned to remove dirt and grease, rinsed and deoxidized with the working solution of the composition given above at 16 oz./gal. and 75 F. for minutes, rinsed in cold water and air dried.

4 The average surface resistance obtained with various aluminum alloys is as follows:

SURFACE RESISTANCE VALUES (MICROHMS, AVERAGE OF FIVE READINGS) OBTAINED WITH VARIOUS ALU- MINUM ALLOYS Initial Surface resistance Aluminum alloy surface resistance after 24 hours (2) Deoxidizing etched aluminum sulfaces MINUM ALLOYS THAT HAVE NOT BEEN HEAT TREATED Initial Surface resistance Aluminum alloy surface resistance after 24 hours EXAMPLE 2 A solid granular composition containing surfactants is prepared by intermixing the following ingredients:

Ingredients: Percent by weight Ferric sulfate 69.0 Sodium nitrate 15.0 Sodium bisulfate 10.0 Sodium silicofiuoride 1.0 Aliphatic polyether (Antarox BL-330) 1.0 Doceyl benzene sulfonic acid 1.0 Isooctyl phenyl polyethoxy ethanol (OPE) 9-10) (Triton X-) 1.0 Ethylene glycol ethyl ether (Dowanol EE solvent 2.0

A desmutting working solution is prepared by dissolving the composition in water at 6 oz./gal. (pH 1.6- 1.7) and heating the solution to 160 F.

Prior to desmutting, the aluminum surfaces are precleaned to remove dirt and grease, rinsed with water, etched with a 6 oz./gal. alkali solution at F. and rinsed with water. The aluminum is then desmutted with the previously prepared working solution. Desmutting times obtained are as follows:

Aluminum alloy:

1100-010-15 secs. 2024-T3-3-3l/2 mins. 3003-0-1 min. 5052-030 secs. 606lT6-2 /23 mins. 6063-T6-l0-l5 secs. 7075-T6-2%-2% mins.

Even better desmutting is obtained at 8 oz./gal. of the composition in the working solution.

The composition of this example can also be used to simultaneously clean and deoxidize aluminum surfaces.

A combination cleaning-deoxidizing solution is prepared by adding 6 ounces of the composition per gallon of water and heating the solution to F. Treatment times of 5-10 minutes are suitable after which the aluminum is rinsed with cold water and air dried. By using this procedure, the results reported in the following table are obtained.

SURFACE RESISTANCE VALUES (MICROHMS-AVERAGE ggYFSIVE READINGS) OF UNETCHED ALUMINUM AL- min. treatment min. treatment Initial Initial surface Value surface Aluminum resistance after resistance alloy value 24 hrs. value 5 11 12 5 50 6 20 39 370 75 600 1 1 11 37 5 34 8 69 7 44 12 72 5 15 8 22 7 075-T6 6 19 8 61 Alclad 7075-16 12 88 6 75 All alloys cleaned satisfactorily without pitting or discoloration.

Using the working solution at 140 F. usually requires a 10 minute treatment. Treatment at 180 F. for 5 minutes is also satisfactory but discoloration or smut may form with some alloys such as 2024-T3 and 7075-T6 aluminum but treatment below 5 minutes at 180 F. is generally suitable for these alloys. At 200 F. discoloration and smut form on some alloys so use of the working solutions at this temperature is not recommended.

EXAMPLE 3 Granular solid mixtures having the following compositions are prepared:

Percent by weight Ingredients A C Ferric sulfate. 59.0 59.0 75. 0 Sodium hisulfate. 21.0 21.0 20.0 Sodium nitrate. 15. 0 15. 0 Sodium bifluoride 5. 0 5. 0 Sodium silicofiuoride 5. 0

Aluminum coupons are precleaned to remove dirt and grease and then deoxidizcd in solutions of compositions A, B and C at 16 oz./ gal. at 75 F. for 5 minutes, rinsed with cold water and dried. The surface resistance of the unetched aluminum coupons is then measured (average of five readings) with the result reported in the following table.

6 and deoxidizing the coupons with working solutions of Compositions A and C at 15 oz./gal. and 75 F. for 5 minutes. The following results are obtained.

SURFACE RESISTANCE VALUES (MICROHMS-AVEBAGE OF 5 READINGS) OF ETOHED ALUMINUM ALLOYS Initial After Initial After Aluminum Alloy value 24 hours value 24 hours The data shows Composition A gives better deoxidization than Composition C.

What is claimed is:

1. A solid composition for dissolving in water for desmutting aluminum and aluminum alloys, said composition consisting essentially of:

Percent by weight Ferric sulfate -75 Alkali metal bisulfate 5-30 Alkali metal nitrate 5-24 Alkali metal silicofiuoride 1-8 2. A solid composition according to claim 1 in which the ingredients are within the ranges:

Percent by weight Ferric sulfate 50-70 Alkali metal bisulfate 15-25 Alkali metal nitrate 10-20 Alkali metal silicofiuoride 1-5 3. A composition according to claim 2 in which the alkali metal in each ingredient is sodium.

4. A solid composition according to claim -1 having the composition:

Percent by weight Ferric sulfate 59-69 Sodium bisulfate 10-21 Sodium nitrate 10-20 Sodium silicofiuoride 1-5 5. A working aqueous solution for desmutting aluminum and aluminum alloys consisting essentially of about 4.0 to 45.0 g. of nitrate ions supplied as an alkali metal nitrate per gallon of solution, about 0.4 to 15.0 g. of fluoride ions supplied as an alkali metal silicofiuoride per SURFACE RESISTANCE VALUES (MICROHMS-AVERAGE OF FIVE READ- INGS) OF UNE'ICHED ALUMINUM ALLOYS No pitting was noted on any of the deoxidized aluminum coupons. Compositions B and C, both of which contain sodium bifluoride, produced a dark smut on the deoxidized 606l-T6 aluminum. Component A, which contains sodium silicofiuoride, did not produce any smut.

Sodium silicofiuoride, present in Composition A, gave markedly better deoxidizing results than sodium bifluoride used in Compositions B and C.

The deoxidizing ability of Compositions A and C on etched non-heat treated aluminum alloys is determined by Ferric sulfate 50-75 precleaning aluminum coupons to remove dirt and grease, Alkali metal bisulfate 5-30 etching the coupons with an alkali solution at 6 oz./gal. Alkali metal nitrate 5-24 and 150 F. for 3 minutes, rinsing the coupons with water Alkali metal silicofiuoride 1-8 7. A method of desmutting aluminum including aluminum alloys which comprises contacting the aluminum surface with an aqueous solution consisting essentially of about 4.0 to 45.0 g. of nitrate ions supplied as an alkali metal nitrate per gallon of solution, about. 0.4 to 15.0 g. of fluoride ions supplied as an alkali metal silicofluoride per gallon of solution, about 0.4 to 2.0 g. of hydrogen ions supplied by an alkali metal bisulfate per gallon of solution and about 8.0 to 60.0 g. of ferric ions supplied as ferric sulfate per gallon of solution.

8. A method of desmutting aluminum including aluminum alloys which comprises contacting the aluminum surface with an aqueous solution containing about 2 to 16 ounces per gallon of solution of a composition consisting essentially of:

Percent by weight Ferric sulfate 50-75 Alkali metal bisulfate -m 5-30 Alkali metal nitrate 5-24 Alkali metal silicofluoride 1-8 References Cited UNITED STATES PATENTS 2,975,039 3/1961 Elliott 156-22 3,326,803 6/1967 Kelly et a1 134-3 XR 3,373,114 3/1968 Grunwald 252-79.1

MAYER WEINBLATT, Primary Examiner US, Cl. X.R. 

